Stefan M.

This plugin will set all Trackbacks and Pingbacks automatically to DoFollow Links.
The user comments will get after <code>X</code> comments from a unique mailaddress automatically DoFollow status. All other comments have NoFollow, except the Admin enable manually the DoFollow Status. The status which is set manual (if DoFollow or NoFollow) will overrides the automatical process. So, you have the control if someone gets sooner the DoFollow status, or never maybe. Of corse, the automatism can be disabled to do the hole work manually.
You get an support automatism, that you don’t need to check daily, but have the full control power.
Additonal this plugin validated all DoFollow URLs and will notice if there are broken links. Broken Links are very bad the Rank in the Search Engines (SEO).
Home Page of the Plugin: <a href="http://blog.murawski.ch/2010/09/wordpress-manual-dofollow-plugin/" title="IT Blögg - WordPress Manual DoFollow Plugin" rel="nofollow ugc">IT Blögg – WordPress Manual DoFollow Plugin</a>
If you have a wish for new functions, please contact me.

SMu Manual DoFollow

SMu DoFollow has many DoFollow Options (Manual or Automatism) and included URL Validator (Manual, WP-Cron or Cronjob).

apasionados

netconsulting

Ansystem

nunsys

This WordPress plugin gives you the possibility to remove the “nofollow” attribute from your wordpress blog’s comments: from the author’s links and/or from the comments text links. This can be done either case by case (editing each comment) or through a white-list of commenters emails, whose comments will allways be dofollow.
And don’t forget:
<blockquote>
Don’t use this plugin if you are using another plugin with similar funcionality. Please read the information about it in the <a href="https://wordpress.org/plugins/dofollow-case-by-case/faq/" title="FAQ section" rel="ugc">FAQ section</a>.
</blockquote>
<h4>What can I do with this plugin?</h4>
This plugin allows you to set links in comments to be dofollow instead of nofollow. When editing a comment, now you have the option to remove the rel=”nofollow” attributes from the links contained in them. 
To make it easier, you can also setup commenters emails whose links in comments should always be dofollow and you can even set their Author URL when commenting to be dofollow. 
On the other side you can also define URLs that when contained in a comment are always dofollow, so that you can setup links to your own sites to be always dofollow.
In order to add commenter’s emails or URLs to the white list, please go to DoFollow > DoFollow.
DoFollow > White List Email: The Email White List contains a list of emails of commenters, whose links in comments are allways dofollow. And you can also choose to make the Author URL dofollow. By default the Author URL is not followed. 
Here you can add for example the email addresses of your staff and collaborators.
DoFollow > White List URL: The URL White List contains a list of URLs that when linked to in a comment, are always dofollow, nevertheless who links to them. 
Here you can setup for example links from your sites or from other sites.
<h4>What ideas is this plugin based on?</h4>
We were looking for a plugin like <a href="https://wordpress.org/plugins/nofollow-case-by-case/" title="Nofollow Case by Case" rel="ugc">Nofollow Case by Case</a> but that worked the other way round. Instead of removing the re=”nofollow” from all comments links and have the possibilty to add the rel=”nofollow” case by case, we wanted to leave the rel=”nofollow” and all comments and have the possibility to remove them only from some comments.
And the last plugin we liked is <a href="https://wordpress.org/plugins/smart-dofollow/" title="Smart DoFollow" rel="ugc">Smart DoFollow</a> which lets you automatically give DoFollow links to authors of comments that are longer than a given number of chars. This is intersting, but very dangerous as today all comment spam is quite long and has many characters.
<h4>DoFollow Case by Case Plugin in your Language!</h4>
This first release is avaliable in English and Spanish. In the i18n we have included the necessarry files to translate this plugin.
If you would like the plugin in your language and you’re good at translating, please drop us a line at <a href="http://apasionados.es/contacto/index.php?desde=wordpress-org-dofollow-home" rel="nofollow ugc">Contact us</a>.
<h4>Further Reading</h4>
You can access the description of the plugin in Spanish at: <a href="http://apasionados.es/blog/dofollow-case-by-case-1676/" rel="nofollow ugc">DoFollow Case by Case en castellano</a>.
<h3>Contact</h3>
For further information please send us an <a href="http://apasionados.es/contacto/index.php?desde=wordpress-org-dofollow-contact" rel="nofollow ugc">email</a>.

DoFollow Case by Case

DoFollow Case by Case allows you to selectively apply dofollow to comments and make links in pages or posts "nofollow".

SMu Manual DoFollow vs DoFollow Case by Case